Apparatus for moistening mixable materials

ABSTRACT

The invention relates to methods of controlling the moistening of mixable materials and to apparatus for carrying out the methods. The invention is particularly applicable to the moistening of foundry casting sand with water. In one method of high-speed low-inertia auxiliary mixing tool is rotated in the sand and the quantity of water added is determined in dependence on the resistance of the sand to rotation of the tool as measured by the power consumption of an electric motor driving the tool. Also disclosed is apparatus for carrying out the method automatically.

United States Patent 1 Ahrenberg 1 APPARATUS FOR MOISTENING MIXABLEMATERIALS [76] lnventor: Kurt Ahrenberg, l-Iuettenweg 5, l-lerborn,Germany [22] Filed: Nov. 13, 1969 [21] Appl. No.: 876,461

[30] Foreign Application Priority/Data Nov. 15, 1968 Germany ..P 18 08998.0

[52] US. Cl. ,.259/154, 259/168, 259/174, 259/177 R [51] Int. Cl ..B28c7/04 [58] Field of Search ..259/l49, 154, 161,

[56] References Cited UNITED STATES PATENTS 3,359,766 12/1967 Haas..68/l2 R X 3,497,884 3/1970 Tichy et a]. ....68/12 R X Eirich et a1Warmkessel 4/1968 Eirich etal ..259/85 3 ,249,970 5/1966 3,109,63211/1963 2,904,401 9/1959 Booth ..23/188 FOREIGN PATENTS OR APPLICATIONS49,771 8/1966 Germany ..259/179 Primary Examiner-Robert W. JenkinsAssistant Examiner-Philip R. Coe Attorney-McGlew and Toren [57] ABSTRACTThe invention relates to methods of controlling the moistening ofmixable materials and to apparatus for carrying out the methods. Theinvention is particularly applicable to the moistening of foundrycasting sand with water. In vone method of high-speed low-inertiaauxiliary mixing tool is rotated in the sand and the quantity of wateradded is determined in dependence on the resistance of the sand torotation of the tool as measured by the power consumption of an electricmotor driving the tool. Also disclosed is apparatus for carrying out themethod automatically.

14 Claims, 5 Drawing Figures COMPUTER /52 PATENTED APR 1 7 7 WW 1 0F 5IN VE N TOR KurtAI-RENBERG PATENTED APR 1 71975 SHEEI 2 OF 5 m VEN TORKqrtAHRENBERG b awn im Hnnvsys PATENTED APR 1 71973 SHEET 3 [IF 5Ell-.2.

h I I I I I L 1A a1: Q27 v I N VENTOR KMAHRENBERG BACKGROUND OF THEINVENTION For the purpose of determining the moisture content ofmoulding sands for casting, it is known to use measuring capacitors, orto pass a test amount of the sand over a plate provided with slots ofdifierent widths, the moisture content being determined in dependence onthe amount of sand which falls through the slots, relative to the amountremaining on the plate. Finally, it is known to determine the moisturecontent of the sand by a cone test.

The above-mentioned known methods suffer either from the disadvantagethat it is not possible to impart a predetermined consistency to thesand, or that test samples must frequently be taken from the sand, whichinterrupts the treatment.

SUMMARY OF THE INVENTION One object of the present invention is toprovide an improved apparatus for controlling the moistening of mixablematerials such as foundry moulding sand.

Another object is to provide such an apparatus in which the quantity ofmoistening liquid added is determined in dependence on the resistance ofthe material to an auxiliary mixing tool.

Another object is to provide such an apparatus in which the auxiliarymixing tool is a high-speed low-inertia rotary mixing tool.

According to the present invention apparatus for moistening a mixablematerial, comprises a container for the material, a main mixing tool formixing the material, a high-speed low-inertia auxiliary mixing tool,driving means to rotate the auxiliary tool in the material, and means toadd a quantity of moistening liquid to the material determined independence on the power consumption of said driving means.

Preferably the auxiliary mixing tool rotates at a speed which is higherby a multiple than the main mixing tool, for example at a peripheralspeed of from to 70 metres per second.

With the apparatus of the invention the following advantages may beobtained.

Because the resistance of the material to a tool which rotates at highspeed is comparatively large, the power consumption of the driving meansfor the auxiliary mixing tool is large, thus permitting an accuratecomparison between the actual and required values, that is, between theactual and required consistency of the material.

Controlling the consistency of the material by automatic moistening ofthe material may be carried out with greater precision, and theapparatus required for that purpose is simplified.

The temperature of the material may if desired be taken intoconsideration at the same time.

Depending on the consistency of the material, which can for examplecomprise moulding sand, ceramic material, concrete, lime sandstonematerials, granulated materials, and pressing and ramming materials, theresistance to mixing and the power consumption may be in widelydifferent ranges. It is therefore advantageous for the driving means forthe auxiliary mixing tool to be a variable speed electric motor,preferably a pole-changing motor. In this way, depending on theconsistency of the material or the nature of individual components ofthe material, the most favourable treatment for each particular case canbe achieved.

Finally, care should be taken that the moisture introduced into themixing material to achieve a predetermined consistency does not exceedits desired value unless additional apparatus is provided for O removingmoisture. It is therefore important that the moisture be distributedrapidly in the material; as otherwise, under certain circumstances, anexcessively low power consumption may momentarily be indicated and anincorrect control order be transmitted to the regulating apparatus,resulting in the further excessive addition of moisture. A regulatingsignal corresponding to the power consumption of the motor mustpreferably therefore be derived when almost unvarying conditions areobtaining in the apparatus, that is, in particular, when the tool isrotating at a speed which is uniform and therefore free fromacceleration, and the material is sufficiently homogenised forcontinuation of the mixing operation not to vary the power consumptionof the motor.

In order to ensure that the further addition of moisture is only derivedfrom the power consumption signal after a substantially unvaryingcondition of the above-mentioned nature has been achieved, the apparatusfor carrying out a two-stage method in which a given amount of moistureis firstly introduced into the material and, subsequently, furthermoistening is controlled in dependence on the power consumption of themotor, can with advantage be embodied with a regulating. apparatus whichhas an adjustable time delay operable after the first supply ofmoisture. This time delay can be made correspondingly larger when thetime constants in the control circuit affect the measurement, so thatthe measured values of the power consumption are in fact taken asconsistency values measured in the substantially unvarying condition ofthe material, and are transmitted to the regulating apparatus for thepurposes of further controlling the moistening operation.

BRIEF DESCRHIPTION OF THE DRAWINGS Two embodiments in accordance withthe invention will now be described by way of example with reference tothe accompanying drawings, in which:

FIG. ll shows the first embodiment in diagrammatic form,

H6. 2 shows the second embodiment in block form, and

FIGS. 3 to 5 show the electric circuit of the second embodiment, thecircuit being completed by placing FIG. 41 to the right of FIG. 3, andFIG. 5 to the right of FIG. 4i.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. l, acounter-flow mixer comprises a clockwise-rotating mixing container 2 inwhich operates a relatively low-speed anti-clockwise-rotating mainmixing tool A having a plurality of mixing blades, and a high-speedlow-inertia auxiliary mixing tool B. The container 2 is rotated by agear motor 29 which drives a ring gear 212 secured to the container. Theaxes of rotation of both tools A and B are eccentric relative to theaxis of rotation of the container 2, and the tool B lies outside theworking area of the tool A.

In operation, a known amount 1 of material to be mixed and moistened isput into the container 2 and treated with an amount 3 of fluid.Hereinafter the material will be assumed to be casting sand and thefluid water. In a first mixing stage, which is not necessarilyregulated, the amount of water is metered by a meter 14 controlling avalve in such a way that, together with the usual initial water contentof the sand, the sand is still definitely below the desired final watercontent necessary to achieve the desired consistency or plasticity. Thisfirst stage prepares for the subsequent stage of finely regulating thewater content, and also brings the water content to a value at which theelectric current or power used by an electric motor 4 driving the tool Bcan be satisfactorily measured.

The sand is then homogenised by the tools A and B, during which stepmany materials have a tendency to increase in volume up to an expansionlevel 6. For clarity, the levels 3 and 6 are shown in exaggerated form.Further high-speed tools, combined with stationary tool systems, canalso be used instead of the tools A and B. The uniform distribution ofthe water can be achieved in a short period of, for example, 10 toseconds, after which time a magnetic valve 7 controlled by a time relay13 opens, so that valves 8a to 8d are acted upon by water pressure.

The power used by the motor 4 in driving the tool B is then measured bya power measuring means having contacts 10a to 10d. There is normallyconnected between the motor 4 and the power measuring means a measuredvalue treatment unit 11 by means of which the measured value istransformed and smoothed. When the sand is homogenous the power used bythe motor 4 is a direct, generally non-linear, function of theconsistency of the sand. As the motor 4 is driven by a constant networkvoltage, the reading of the power measuring means is proportional to thecurrent used and causes one or more of the contacts 10a to 10d to betripped so that the measured value which is obtained in analog form isquantised in four steps. Depending on the number of contacts 10a to 10dtripped, a control unit 12 acts on the magnetic valves 80 to 8d in sucha way that any of the contacts 10a to 10d tripped cause thecorresponding valves 8a to 8d to be opened.

The amount of water allowed into the sand during this second stagedepends on the condition of the valves 80 to 8d, the common supply pipe16 to which is throttled after a predetermined period by the magneticvalve 7. In this way, the amount of water added depends on the number ofvalves 8a to 8dopen, and this is determined by the consistency of thesand following the first stage. Following the addition of the water inthe second stage the sand is again homogenised and subsequentlydischarged. All the control and regulating elements are then returned totheir initial conditions.

The above described method and the apparatus can be modified in variousways without going outside the scope of the invention. Thus the valves8a to 8d could be closed by flow measuring means instead of the timerelay 13. Depending on the specific use to which the apparatus is put,the valves 8a to 8d can also be formed as regulating valves, regulatingcocks, snap valves or restrictor valves with a large flow cross-sectionif thick or viscous fluids are used for moistening. The valve controlcan be effected by potentiometers which fully open the valves initiallyand then successively close them in dependence on the power used by themotor 4.

If the motor 4 is a three-phase motor, the abovementioned powermeasuring means will desirably be used, while with a direct-currentmotor a contact ammeter is preferable. When hydraulic motors are used todrive the tools A and B, they are combined with known regulating andmeasuring devices.

The invention permits reliable control of the moistening operation andrapid homogenisation of the sand. By using a constant weight of sand ahigh degree of measuring precision can be achieved because of thepossibility of reproducing the values of power used relative to a givenwater content, and hence calibrating the power measuring means. Also, ahigh-speed low-inertia auxiliary tool has a sensitive reaction tovariations in water content of the sand, so that the range of power usedis extended and differentiation between different water contentsincreased. The sensitivity and precision of the regulation is stillfurther increased if the motor 4 is connected directly, that is withoutthe interpolation of gears, to the tool B/Additionally, it has beenfound advantageous if the motor 4 maintains its speed of rotationsubstantially constant within the measuring range. As differentmeasuring ranges are found desirable for different materials, it is ofadvantage for the motor 4 to be pole-changing.

It has been found preferable for the tool B to be in the form of aH-shaped spinner 5, the bars of which diverge upwardly in a V-shape.However other tools suited to the specific properties of the materialcan also be used.

in the apparatus shown in FIGS. 2 to 5, two limit contacts areassociated with the power measuring means W coupled to the motor 4 forthe auxiliary tool B. With the two limit contacts in this embodiment, afour-stage mode of operation is achieved by means of a suitable circuitconnected to the power measuring means W and in this way the requiredwater content can be approached in steps.

In order to make the cycle time of the mixer as short as possible, theapparatus should be set very rapidly and automatically to the watercontent which is still missing from the material. The amount of water inthe old sand which is found for example in foundries, can however varywithin wide limits. If for example the water content in the sand whichhas not yet been treated is in the vicinity of the required value, thefirst stage, which generally adds a large amount of water, and possiblyeven the second stage, are omitted so that then only the third andfourth stages are operative, with correspondingly smaller amounts ofwater added. The

sequence in time of the additions of water and the amounts of water tobe added can therefore be adjusted as desired as will now be described.

in H6. 2, the container 2 is shown diagrammatically with a main mixingtool A and a spinner or auxiliary tool B, the motor 4 of which iscoupled to the power measuring means W. The power measuring means Wtransmits a signal to a pulse transmitter U1 which actuates the countingcircuit Z. The counting circuit Z is connected to a transmitter U3 whichactuates a magnetic valve V for the required water supply periods andintervals The magnetic valve V can be actuated in four modes by thetransmitter U3 in the embodiment shown, the variation in the supplyperiods and intervals in each mode resulting in a variation in theamount of water added. With the shortest supply period and the longestinterval, the throughput is 0.25 litres per minute, whilst with thelongest supply period and the shortest interval, the throughput is 60litres per minute.

The mode of operation of the metering control cir' cuit with four-stageautomatic operation will now be described with reference to FIGS. 3 to5. The metering operation is initiated when a switch B1 in the currentpath 12 is temporarily closed. This results in the relay 11A beingenergised, whereby the contacts DlA in the current path 39 are closed.This results in the control voltage for the metering apparatus beingconnected.

The relay d3 in the counting circuit Z is energised by way of the restcontacts D2/0 in the current path 18 The relay d3 closes inter alia thecontact D3 in the currentpath 24 which'supplies voltage to twopotentiometers (not shown) of the transmitter U3, which serve to adjustthe water-supply period and interval of the first mixing stage. Thesetwo potentiometers are built into the transmitter U3 together with theinterval potentiometers of the second, third and fourth mixing stages.Therefore, for each stage there is provided a potentiometer foradjusting the supply period of the valve V and a potentiometer foradjusting the interval. The transmitter U3 therefore acts as a pulsetransmitter with variable supply periods and intervals. The intervalsmust be selected in such a way that the water which is added during thefirstsupply period of the magnetic valve'V mixes thoroughly with thesand. Only then does the power measuring means W indicate a rise inpower consumption by the motor 4, and only after the power rise hasterminated should the second addition of water take place.

Owing to the relay d3 being energised, the contact D3 in the currentpath 35 is also closed, energising the relay dl2. As a result, the restcontact D12 in the current path 43 is opened, which opens the circuit ofthe voltage path for the power measuring means W, which path includesthe resistor R1. At the same time the working contact D12 in the currentpath 43 is closed, which closes the voltage path by way of the variableresistor R3 and the resistor R2. A voltage varied for example by 20percent can be delivered to the power measuring means W by the resistorR3. By means of such an increase in voltage in the voltage path, theindication of the indicator (not shown) of the power measuring means Wcan be made to exceed the actual power consumption of the motor 4.

Asfalready mentioned, the closed contact D3 in the current path 24passes voltage to the two potentiometers for the first stage and by thecontact 143 of the transmitter U3, the valve relay d9 in the currentpath 28 is energised and de-energised according to the supply periodsand intervals set in the two potentiometers. Accordingly, the supply ofwater to the sand is effected by the valve V. For this pu'rpose, thevalve relay d9 switches the contacts D9 in the current path 11 whichincludes the valve V.

consumption by the motor 4 and the indicator of the power measuringmeans W leaves the minimum mark,

whereupon the relay d14 in the current path 41 is energised. The contactD14 in the currentpath 31, which is supplied with voltage by way of theclosed contact D15 of the relay d15, energises the relay d1 1 in by wayof the contact D3 which is also closed by the relay d1 1. The restcontact D11 in the current path 28 then opens and de-energises the valverelay 9. The working contact D11 in the current path 16 is closed at thesame time by the relay d1 1 and transmits voltage to the terminal 5 ofthe transmitter U1.

The transmitter U1 is also a pulse transmitter with variable workingperiods and interval. The working period of the pulse transmitter U1 isset to be very short as it acts to restrict the transmission of pulses,while the interval period acts as a response delay, so that theindicator of the power measuring means W is generally not quite at restin operation of the metering apparatus, and so that its first maximumdeflection should not initiate any stepping of the counting circuit Z.In other words, the supply of water to the sand should be stopped atthat moment, but the pulse transmitter U1 should not yet step thecounting circuit Z on to the next I stage.

When the indicator of the power measuring means W has finally moved offthe minimum mark, the contact ul of the transmitter U1, which contact ullies in the current path 14, closes temporarily, and the coil 42 of thecounting circuit Z which also lies in the current path 14 is energised.As a result, the counting circuit Z is stepped on by one step. Theresult of this is that the rest contact D2/0 opens and the workingcontact D2/1 in the current path 19 closes. The contact D2/1 energisesthe relay d4 in the current path 19, of which the working contact D4which is in the current path 25 then closes and transmits voltage tothe-two potentiometers for the supply periods and intervals of thesecond stage. The transmitter U3 energises and deenergises the valverelay d9 according to the valves set by way of the contact 143, and thewater supply of the second stage takes place.

Owing to the relay d3 becoming deenergised, the relay dl2 is alsode-energised by way of the contact D3", the contacts D12 and D12 of therelay d12, which lie in the current path 43, switching the voltage pathof the power measuring means W to normal voltage. As a result of thisswitch to normal voltage, the indicator of the power measuring means Wreturns to the minimum mark and the relay d14 becomes de-ener-.

gised, the contact D14 opening. At the same time the contact D3 in thecurrent path 31 opens and de-energises the relay dll. The rest contactD11 of the relay dll which lies in the current path 28 prepares for theenergising of the valve relay d9. The working contact D1 1 of the relayd3 simultaneously interrupts the control voltage for the transmitter U1so that further stepping on of the counting circuit Z is prevented.

At this moment, the power measuring means W is operating withoutincreased voltage. If now the power consumption of the motor 4 is againincreased by the supply-of water in the second stage, the indicator ofthe power measuring means W again moves off the minimum mark. The relaydl4 is again energised and its working contact D14, which is in thecurrent path 31, energises the relay d1 1 by way of the contact D4 inthe current path 32, which contact has already been closed by the relayd4. The rest contact D11 of the relay dll de-energises the valve relayd9. The working contact D11 is closed at the same time and transmitscontrol voltage to the transmitter U1. The transmitter U1 steps thecounting circuit Z by a further step, as already described above.

In that case, the relay d4 becomes de-energised and the relay d of thecounting circuit Z is energised by way of the closed contact D2/2. Thecontact D4 in the current path 32 opens owing to the relay d4 becomingde-energised and de-energises the relay dll. The working contact D5 isclosed by the relay d5 and transmits voltage to the two potentiometersin the transmitter U3 for the supply periods and intervals of the thirdstage. At the same time, the working contact D5 in the current path 36is closed and transmits voltage to the relay d13 in the same currentpath. The relay dl3 actuates the switching contact D13 and D13 in thecurrent path 44, which interrupts the voltage path of the powermeasuring means W by way of the resistor R1 and switches the latter tothe variable resistor R5. Depending on the particular setting of thelatter, an increased voltage is then again transmitted to the voltagepath of the power measuring means W, which results in an increased powerconsumption indication. From this it is apparent that the voltageincrease in the first and the third stages can be adjusted separately.

The valve relay d9 which actuates the valve V is energised andde-energised, as already mentioned, by the transmitter U3. When theindicator of the power measuring means W finally reaches the maximummark, the relay 1115 in the current path 42 becomes deenergised. Therest contact D of the relay dl5, which lies in the current path 33,closes and energises the relay dll by way of the working contact D5which is already closed. The relay dll de-energises the valve relay d9by way of the contact D1 1 and supplies voltage to the transmitter U1 byway of the contact D1 1 as already described above. As a result, thecounting circuit Z is stepped on by one step. The relay d5 of thecounting circuit becomes de-energised and the relay d6 becomes energisedby virtue of the contact D2/3 being closed. Owing to the de-energisationof the relay d5, the relay 13 in the current path 36 is de-energised byway of the contact D5. Also, the switching contact D13, D13 which liesin the current path 44 and which is actuated by the relay d13 switchesthe voltage path of the power measuring means W back to normal voltage.This condition is shown in FIG. 5. The result of this is that theindicator of thepower measuring means W again moves off the maximum markso that the relay 1115 is again energised.

The two potentiometers in the transmitter U3 for the supply periods andintervals of the fourth and last stage are energised by the relay d6.The transmitter U3 again accordingly actuates the valve relay :19. Thisresults in a further supply of water to the sand and the indicator ofthe power measuring means W again returns to the maximum mark, owing tothe rising power consumption of the motor 4. As a result, the relay d15is again deenergised and its rest contact D15 which is in the voltagepath 33 energises the relay dll by way of the working contact D6 in thecurrent path 34, which contact is already closed by the relay d6. Therelay d1 1 deenergises the valve relay d9 and transmits voltage to thetransmitter U1 by way of the contact D11. The transmitter U1 thereuponsteps the counting circuit Z by a further step. The working contact D2/4of the counting circuit Z, which contact lies in the current path 22,transmits control voltage to the terminal 5 of the reset circuit U2 forresetting the counting circuit Z. The working contact u2 of the circuitU2 which lies in the current path 13, energises the coil dlZ, wherebythe control voltage for the entire apparatus is interrupted by way ofthe contact DlZ in current path 37. The working contact 142 of the resetcircuit U2, which contact lies in the current path 15, transmits ahalfwave rectified voltage by way of the zero-position contact D2 to thecoil 42 which thereupon returns the counting circuit Z to its zeroposition. The pulse transmission of the reset circuit U2 last for about1 second.

After the above switching operation has taken place, the supply of wateris concluded and the apparatus is ready for a new metering operation.

If, by virtue of the power measurement, it turns out that there isinitially a relatively large amount of water in the sand, the variousstages are omitted until the power measuring means W indicates a valuewhich shows that the addition of water is necessary. Manual release ofthe valve relay d9 for corresponding switching of the magnetic valve Vis also possible by way of the manual switches B3 and B4 in the currentpath 30.

Instead of the above described circuit with a power measuring means W,the principle upon which the invention is based can also be embodied bya control circuit having for example a current measuring means with anelectronic coefficient forming means, or any other measuring device forsupplying the necessary measured values. If materials with widelyvarying starting temperatures are to be processed, additionaltemperature sensing means 50 which operate in combination with acomputer 32 are used, in order to correct the influence of temperatureon the amount of water contained in the material.

Various other modifications can be made without departing from theinvention as defined by the appended claims. In particular it is to benoted that the references to sand and water in the specific descriptionare only examples of the materials and liquids with which the inventioncan be used.

lclaim:

1. Apparatus for moistening a mixable material by the multi-stageaddition of a moistening liquid, comprising a container rotatable abouta substantially vertical axis and arranged to hold the material to bemixed and moistened, a vertically arranged relatively lowspeed rotatablemain mixing tool located within said container for mixing the material,a vertically arranged high-speed low-inertia auxiliary mixing toollocated within said container and spaced laterally from said main mixingtoolso that its path of rotation is outside the path of rottion of saidmain mixing tool, driving means for rotating the auxiliary tool in thematerial, means for a step-wise addition of moistening liquid to thematerial to bring its moisture content to a predetermined level, andcontrol means for regulating said means for a step-wise addition ofmoistening liquid to the material determined in dependence on the powerconsumption of said driving means for said auxiliary mixing tool, andsaid control means includes a means for affording an interval in whichthe moistening liquid thoroughly mixes with the material before thepower consumption of said driving means is determined.

2. Apparatus according to claim 1 wherein the driving means is anelectric motor.

3. Apparatus according to claim 2 wherein the auxiliary mixing tool isconnected directly to the electric motor.

4. Apparatus according to claim 3 wherein the rotational speed of theelectric motor is substantially independent of the load thereon.

5. Apparatus according to claim 3 wherein the elec tric motor is avariable speed motor.

6. Apparatus according to claim 3 wherein the electric motor is apole-changing motor.

7. Apparatus according to claim 1 wherein the auxiliary mixing tool isapproximately H-shaped.

8. Apparatus according to claim 1 wherein said control means comprisesmeans operative after the addition of moistening liquid to the materialto prevent the addition of further moistening liquid for a predeterminedtime.

9. Apparatus, as set forth in claim 1, wherein said auxiliary mixingtool is approximately H-shaped and.

the upwardly extending sides of said auxiliary mixing tool converge inthe downward direction.

10. Apparatus for moistening a mixing material, comprising a containerfor the material, a main mixing tool for mixing the material, ahigh-speed low-inertia auxiliary mixing tool, driving means for rotatingthe auxiliary tool in the material, control means for adding a quantityof moistening liquid to the material determined in dependence on a powerconsumption of said driving means for said auxiliary mixing tool, saidcontrol means comprising means for measuring the power consumption ofsaid driving means, said means for measuring the power consumptionincluding devices for sensing the limiting values of the power consumedin each stage of the moistening of the mixable material between aminimum value and a maximum value, an indicator of the power consumed,and means for increasing the power consumed as shown on said indicatorby a predetermined amount relative to the actual power consumption ofsaid driving means, a first pulse generator to which in operation saidmeasuring means supplies a signal, a counting circuit controlled by saidfirst pulse generator and including a plurality of counting stages, asecond pulse generator including means to determine the supply periodsand intervals for the supply of moistening liquid to the material, and amagnetic valve by way of which the moistening liquid is supplied to thematerial, in operation the counting stages supplying signals to saidsecond pulse transmitter to determine the time during which saidmagnetic valve is operated for supplying moistening liquid and saidsecond pulse transmitter determining the supply periods and intervalswithin each stage of the addition of the moistening liquid.

ll. Apparatus according to claim 10 wherein said means in the secondpulse transmitter to determine the supply periods and intervalscomprises potentiometers.

12. Apparatus according to claim 10 wherein the counting circuit hasfour stages and the second pulse transmitter has four stages whereby themoistening liquid can be added in four separately controllable stages.

13. Apparatus, according to claim 10, wherein said first pulsetransmitter is adjustable for variable working periods and intervals.

14. Apparatus, according to claim 10, wherein a reset circuit isarranged for returning said counting circuit to zero, and said resetcircuit being controlled by said counting circuit.

1. Apparatus for moistening a mixable material by the multistageaddition of a moistening liquid, comprising a container rotatable abouta substAntially vertical axis and arranged to hold the material to bemixed and moistened, a vertically arranged relatively low-speedrotatable main mixing tool located within said container for mixing thematerial, a vertically arranged high-speed low-inertia auxiliary mixingtool located within said container and spaced laterally from said mainmixing tool so that its path of rotation is outside the path of rotationof said main mixing tool, driving means for rotating the auxiliary toolin the material, means for a step-wise addition of moistening liquid tothe material to bring its moisture content to a predetermined level, andcontrol means for regulating said means for a step-wise addition ofmoistening liquid to the material determined in dependence on the powerconsumption of said driving means for said auxiliary mixing tool, andsaid control means includes a means for affording an interval in whichthe moistening liquid thoroughly mixes with the material before thepower consumption of said driving means is determined.
 2. Apparatusaccording to claim 1 wherein the driving means is an electric motor. 3.Apparatus according to claim 2 wherein the auxiliary mixing tool isconnected directly to the electric motor.
 4. Apparatus according toclaim 3 wherein the rotational speed of the electric motor issubstantially independent of the load thereon.
 5. Apparatus according toclaim 3 wherein the electric motor is a variable speed motor. 6.Apparatus according to claim 3 wherein the electric motor is apole-changing motor.
 7. Apparatus according to claim 1 wherein theauxiliary mixing tool is approximately H-shaped.
 8. Apparatus accordingto claim 1 wherein said control means comprises means operative afterthe addition of moistening liquid to the material to prevent theaddition of further moistening liquid for a predetermined time. 9.Apparatus, as set forth in claim 1, wherein said auxiliary mixing toolis approximately H-shaped and the upwardly extending sides of saidauxiliary mixing tool converge in the downward direction.
 10. Apparatusfor moistening a mixing material, comprising a container for thematerial, a main mixing tool for mixing the material, a high-speedlow-inertia auxiliary mixing tool, driving means for rotating theauxiliary tool in the material, control means for adding a quantity ofmoistening liquid to the material determined in dependence on a powerconsumption of said driving means for said auxiliary mixing tool, saidcontrol means comprising means for measuring the power consumption ofsaid driving means, said means for measuring the power consumptionincluding devices for sensing the limiting values of the power consumedin each stage of the moistening of the mixable material between aminimum value and a maximum value, an indicator of the power consumed,and means for increasing the power consumed as shown on said indicatorby a predetermined amount relative to the actual power consumption ofsaid driving means, a first pulse generator to which in operation saidmeasuring means supplies a signal, a counting circuit controlled by saidfirst pulse generator and including a plurality of counting stages, asecond pulse generator including means to determine the supply periodsand intervals for the supply of moistening liquid to the material, and amagnetic valve by way of which the moistening liquid is supplied to thematerial, in operation the counting stages supplying signals to saidsecond pulse transmitter to determine the time during which saidmagnetic valve is operated for supplying moistening liquid and saidsecond pulse transmitter determining the supply periods and intervalswithin each stage of the addition of the moistening liquid. 11.Apparatus according to claim 10 wherein said means in the second pulsetransmitter to determine the supply periods and intervals comprisespotentiometers.
 12. Apparatus according to claim 10 wherein the countingcircuit has four stages and the second pulse transmitter has four stageswhereby the moistening liquid can be added in four separatelycontrollable stages.
 13. Apparatus, according to claim 10, wherein saidfirst pulse transmitter is adjustable for variable working periods andintervals.
 14. Apparatus, according to claim 10, wherein a reset circuitis arranged for returning said counting circuit to zero, and said resetcircuit being controlled by said counting circuit.